Chromatic corrected EFTEM investigation on spinodal decomposition of TiAlN at 80 kV with PICO

Abstract

Chromatic aberration (Cc) in the modern transmission electron microscopy (TEM) plays an important role with the advancement the resolution up to atomic level 1 . Correction of Cc is especially important for high resolution energy ‐filtered TEM (EFTEM) with the requirement of large slit width and signal intensity to obtain an atomic resolved image, formatted from the inelastic scattered electrons in a limited time and stability constraint. As an advantage, large area and high resolution elemental map can be obtained in just tens of seconds, much faster than the traditional STEM‐EELS counterpart. The short acquisition time is very crucial in the practical applications of both material science and biological science where the samples are very often sensitive to the electron beam illumination, the interesting compositions and structures are unknown, or they are the mixture of different elements and phases. In this report, an annealed TiAlN sample is prepared for the EFTEM investigation with FEI‐Titan PICO, focusing on the spinodal decomposition phenomenon. As a hard‐coating material, TiAlN has exceptional mechanical and thermal properties attractive for tool‐coating industry 2 . However at a higher temperature around 900 °C, the hardness is found to drop drastically owing to the formation of hexagonal AlN, which typically occurs after the spinodal decomposition. The spinodal decomposition contains the segregation of the composition while the crystal structure remains 3 . It is therefore typically difficult to prove the existence of this phenomenon without an elemental map with an atomic resolution, which is exactly a Cc corrected EFTEM image can provide. In addition, different effects to the image resolution induced from factors considered in a Cc corrected EFTEM experiment will be discussed, including sample thickness, acceleration voltage, sample drifting, and atomic numbers of the sample. Compositional variation near the dislocation will be discussed as well. Preservation of elastic contrast 4 has been observed and analyzed, which is crucial to map the inelastic image into the final elemental map.